Gender refers to the differences between men and women. Encyclopaedia Britannica describes gender identity as "an individuals self-conception as being male or female, as distinguished from actual biological sex". Although gender is sometimes used interchangeably with sex, it is a much broader concept that includes social differences and expectations, known as gender roles. Therefore gender is a phrase that encompasses the way people act and interact with others, and how they feel about themselves, which can include associations with both masculinity and femininity.

Transgender is a general term used to describe individuals whose gender identity, ie. sense of themselves as male or female, differs from that usually associated with their birth sex. Broadly speaking people whose gender identity feels different or incongruent with their physical bodies may call themselves transgender. Transgender individuals may live part-time or full-time as members of the other gender. However, everybody is different and unique, so not everyone who may appear gender-atypical will identify themselves as transgendered.

Transsexuals are transgendered people who desire to live as members of the gender opposite to their birth sex. Biological females who wish to live as men are called female-to male (FTM) transsexuals or transsexual men. Biological males who wish to live as women are called male to female transsexuals (MTF) or transsexual women. Transsexualism, a medical term, is the condition in which a person identifies with the physical sex that is different from their biological one, that is the one they were born with or assigned to. When individuals feel that the way they look on the outside doesn't fit with how they feel on the inside, it is associated with a general feeling of discomfort and unhappiness that is described as gender dysphoria. Gender dysphoria is now a recognised condition for which medical treatment is available under the National Health Service.

Transsexualism is becoming increasingly understood and, although services are limited, the need for specialist professionals and services has been recognised. Research studies have tried to look at the causes and origins and have helped inform professionals about appropriate support and treatments. Involving the Transgender Community in planning this is a vital component of service development and there now exist a number of specialist screening clinics and treatment centres.

The statistics on the prevalence of transsexualism varies considerably. However it has been generally acknowledged that it is far more common than people originally thought. DSM-IV (1994) quoted prevalence of approximately 1 in 30,000 assigned males and 1 in 100,000 assigned females seek gender reassignment surgery in the USA. A population-based study in Amsterdam, which spanned more than four decades treating over 95% of Dutch transsexuals, found figures of 1 in 10,000 assigned males and in 1 in 30,000 assigned females as suffering from gender dysphoria. More recent studies have suggested much higher prevalence rates than this. It may be as common as 1 in 4,500 assigned males and 1 in 8,000 assigned females across a number of different countries around the world. It is likely that the actual prevalence may be even higher than this in the Western world including the UK.